Hybrid electrochemical capacitor

ABSTRACT

Hybrid electrochemical capacitors, electronic devices using such capacitors, and associated methods are disclosed. In an example, a hybrid electrochemical capacitor can include a first electrode made from Mg, Na, Zn, Al, Sn, or Li, a second electrode made from a porous material such as porous carbon or passivated porous silicon, and an electrolyte. The hybrid electrochemical capacitors can have enhanced voltage and energy density compared to other electrochemical capacitors, and enhanced power density compared to batteries.

PRIORITY INFORMATION

This application is a continuation of U.S. patent application Ser. No.14/136,933, filed Dec. 30, 2013, now issued as U.S. Pat. No. 9,640,332,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

Embodiments described herein relate generally to energy storage devices,and relate more particularly to batteries and capacitors.

BACKGROUND

Modern society depends on the ready availability of energy. As thedemand for energy increases, devices capable of efficiently storingenergy become increasingly important. As a result, energy storagedevices, including batteries, capacitors, electrochemical capacitors(ECs), hybrid ECs, and the like are used extensively in the electronicsrealm and beyond. In particular, capacitors are widely used forapplications ranging from electrical circuitry and power delivery tovoltage regulation and battery replacement.

Electrochemical capacitors (including pseudocapacitors and electricdouble-layer capacitors (EDLCs) (sometimes called ultracapacitors, amongother names) are characterized by high energy storage capacity, rapidcharge/discharge ability, and large cycle lifetimes, as well as otherdesirable characteristics including high power density, small size, andlow weight, and have thus become promising candidates for use in severalenergy storage applications. One difference between electrochemicalcapacitors and batteries is that electrochemical capacitors can becharged and discharged quickly because they do not rely on chemicalreactions to store energy, and they don't degrade significantly overtheir lifetime, even when charged and discharged rapidly.Electrochemical capacitors are also less sensitive to temperature thanbatteries. Hybrid ECs combine high power, fast charging capability, andlong cycle life with higher voltages that increase the energy densityover conventional EC capacitors. Hybrid ECs thus bridge the gap betweentraditional electrochemical capacitors and batteries in that they havehigher power density than Li-ion batteries and higher energy densitythan EC capacitors. Also, hybrid capacitors can achieve efficiencies of95% or more which is greater than the 70% efficiency exhibited by manybatteries.

BRIEF DESCRIPTION OF THE DRAWINGS

Disclosed embodiments will be apparent from the detailed descriptionwhich follows, taken in conjunction with the accompanying drawings,which together illustrate, by way of example, various features; and,wherein:

FIG. 1 is a cross-sectional view of a hybrid electrochemical capacitorin accordance with an invention embodiment;

FIG. 2 is a cross-sectional view of a hybrid electrochemical capacitorin accordance with an invention embodiment;

FIG. 3 is a cross-sectional view of a hybrid electrochemical capacitorin accordance with an invention embodiment;

FIG. 4 is a flowchart illustrating a method of manufacturing a hybridelectrochemical capacitor in accordance with an invention embodiment;

FIGS. 5A-5B are charts illustrating cyclic voltammetry tests performedon a hybrid electrochemical capacitor in accordance with variousinvention embodiments.

For simplicity and clarity of illustration, the drawing figuresillustrate the general manner of construction, and descriptions anddetails of well-known features and techniques may be omitted to avoidunnecessarily obscuring the discussion of the described embodiments.Additionally, elements in the figures are not necessarily drawn toscale. For example, the dimensions of some of the elements in thefigures may be exaggerated relative to other elements to help improveunderstanding of the embodiments illustrated. Certain figures may beshown in an idealized fashion in order to aid understanding, such aswhen structures are shown having straight lines, sharp angles, and/orparallel planes or the like that under real-world conditions wouldlikely be significantly less symmetric and orderly. The same referencenumerals in different figures denote the same elements, while similarreference numerals may, but do not necessarily, denote similar elements.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation is thereby intended.

DESCRIPTION OF EMBODIMENTS

Although the following detailed description contains many specifics forthe purpose of illustration, a person of ordinary skill in the art willappreciate that many variations and alterations to the following detailsare within the scope of the herein disclosed invention embodiments.

Accordingly, the following invention embodiments are set forth withoutany loss of generality to, and without imposing limitations upon, anyclaims set forth herein. Before any invention embodiments are describedin greater detail, it is to be understood that this disclosure is notlimited to the particular invention embodiments described. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular invention embodiments only, and is not intended tobe limiting. Unless defined otherwise, all technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this disclosure belongs.

As used in this specification and the appended claims, the singularforms “a,” “an” and “the” include plural referents unless the contextclearly dictates otherwise. Thus, for example, reference to “a porousmaterial” includes a plurality of such materials.

In this disclosure, “comprises,” “comprising,” “containing” and “having”and the like can have the meaning ascribed to them in U.S. Patent lawand can mean “includes,” “including,” and the like, and are generallyinterpreted to be open ended terms. The term “consisting of” is a closedterm, and includes only the components, structures, steps, or the likespecifically listed, and that which is in accordance with U.S. Patentlaw. “Consisting essentially of” or “consists essentially” or the like,when applied to methods and compositions refers to compositions likethose disclosed herein, but which may contain additional structuralgroups, composition components or method steps. Such additionalstructural groups, composition components or method steps, etc.,however, do not materially affect the basic and novel characteristic(s)of the compositions or methods, compared to those of the correspondingcompositions or methods disclosed herein. In further detail, “consistingessentially of” or “consists essentially” or the like, when applied tomethods and compositions disclosed herein have the meaning ascribed inU.S. Patent law and the term is open-ended, allowing for the presence ofmore than that which is recited (e.g., trace contaminants, componentsnot reactive with porous silicon substrate, and the like) so long asbasic or novel characteristics of that which is recited is not changedby the presence of more than that which is recited, but excludes priorart embodiments. When using an open ended term, like “comprising” or“including,” it is understood that direct support should be affordedalso to “consisting essentially of” language as well as “consisting of”language as if stated explicitly.

The terms “first,” “second,” “third,” “fourth,” and the like in thedescription and in the claims, if any, are used for distinguishingbetween similar elements and not necessarily for describing a particularsequential or chronological order. It is to be understood that the termsso used are interchangeable under appropriate circumstances such thatthe embodiments described herein are, for example, capable of operationin sequences other than those illustrated or otherwise described herein.Similarly, if a method is described herein as comprising a series ofsteps, the order of such steps as presented herein is not necessarilythe only order in which such steps may be performed, and certain of thestated steps may possibly be omitted and/or certain other steps notdescribed herein may possibly be added to the method. Furthermore, theterms “comprise,” “include,” “have,” and any variations thereof, areintended to cover a non-exclusive inclusion, such that a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to those elements, but may include other elementsnot expressly listed or inherent to such process, method, article, orapparatus.

The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,”“under,” and the like in the description and in the claims, if any, areused for descriptive purposes and not necessarily for describingpermanent relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances such that theembodiments described herein are, for example, capable of operation inother orientations than those illustrated or otherwise described herein.The term “coupled,” as used herein, is defined as directly or indirectlyconnected in an electrical or nonelectrical manner. Objects describedherein as being “adjacent to” each other may be in physical contact witheach other, in close proximity to each other, or in the same generalregion or area as each other, as appropriate for the context in whichthe phrase is used. Occurrences of the phrase “in one embodiment” hereindo not necessarily all refer to the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and examples may be referredto herein along with alternatives for the various components thereof. Itis understood that such embodiments, examples, and alternatives are notto be construed as de facto equivalents of one another, but are to beconsidered as separate and autonomous.

As used herein, “electrolyte” and “ion containing electrolyte” may beused interchangeably and include solid electrolytes, gel electrolytes,ionic liquids, and liquid electrolyte solutions, including aqueous basedand organic based liquids unless otherwise specified.

As used herein, “substantial” and “substantially” when used in referenceto a quantity or amount of a material, or a specific characteristicthereof, refers to an amount that is sufficient to provide an effectthat the material or characteristic was intended to provide.

The exact degree of deviation allowable may in some cases depend on thespecific context. Similarly, “substantially free of” or the like refersto the lack of an identified element or agent in a composition.Particularly, elements that are identified as being “substantially freeof” are either completely absent from the composition, or are includedonly in amounts which are small enough so as to have no measurableeffect on the composition.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment. Thus,appearances of the phrases “in an example” in various places throughoutthis specification are not necessarily all referring to the sameembodiment.

EXAMPLE EMBODIMENTS

An initial overview of technology embodiments is provided below andspecific technology embodiments are then described in further detail.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key or essentialfeatures of the technology, nor is it intended to limit the scope of theclaimed subject matter.

The energy density of a hybrid electrochemical capacitor (EC) can beincreased by increasing the electrical potential over that of aconventional EC. This can be achieved by using a high surface-areaporous material for the cathode and a battery-like electrode for theanode. In one embodiment, a hybrid electrochemical capacitor comprises afirst electrode that includes Mg, Na, Zn, Al, or Sn and a secondelectrode comprising a porous material or a nanostructure having asurface-area-to-volume ratio of at least 10 m²/cm³, along with anelectrolyte and a separator. In some embodiments, thesurface-area-to-volume ratio of the porous material can be from about 10m²/cm³ to about 5000 m²/cm³; in other embodiments the ratio can be fromabout 100 m²/cm³ to about 2000 m²/cm³; and in other embodiments theratio can be from about 300 m²/cm³ to about 1000 m²/cm³. In anotherembodiment, the first electrode comprises Mg, Na, Zn, Al, Sn, Li,pre-lithiated porous carbon, or pre-lithiated soft carbon. Porous carbonor soft carbon can also be pre-impregnated with metal ions other thanLi. The second electrode can comprise porous silicon suitably passivatedwith a material, in some instances, a conductive material.

Hybrid ECs in accordance with certain embodiments can be integrated intosilicon devices or onto packages in order to provide energy storage withrapid response. They can be used in conjunction with batteries or(potentially) to replace batteries in applications such as: power forsleep/standby modes or backup power for memory (where they can be usedrepeatedly due to the high cycle lifetime); quick charge, turbo mode,and camera flash; low temperature applications (operating range of −25°C. to +60° C. with less than 5% energy loss (versus 50% for batteries));energy harvesting devices; automotive applications (emergency power(e.g., for unlocking doors or lowering windows), sufficient powerdensity for up-hill or accelerative driving; regenerative brakingprovides some recharging); and others. In addition, hybrid ECs arecompatible with intermittent renewable energy sources (wind-turbines,solar/photovoltaic panels, hydraulic power, wave generators, etc.).Hybrid ECs can also be used for small devices such as in wearabletechnology or devices for connecting a multitude of everyday objects,appliances, products, product packaging, etc. to the Internet (to forman “Internet of Things”).

Referring now to the drawings, FIG. 1 is a cross-sectional view of ahybrid electrochemical capacitor 100 in accordance with an inventionembodiment. The hybrid EC has a first electrode 110, a second electrode120, and an electrolyte 130. The first electrode and second electrodecan be spaced apart to avoid electrical shorts between the electrodes.In some embodiments, the first electrode can comprise Mg, Na, Zn, Al,Sn, or combinations thereof, and the second electrode can comprise aporous material having a surface-area-to-volume ratio of at least 10m²/cm³. In some embodiments, the surface-area-to-volume ratio of theporous material can be from about 10 m²/cm³ to about 5000 m²/cm³; inother embodiments the ratio can be from about 100 m²/cm³ to about 2000m²/cm³; and in other embodiments the ratio can be from about 300 m²/cm³to about 1000 m²/cm³. The porous material can have pores 140 opening ata surface of the electrode to allow the electrolyte to enter the pores.In some embodiments, the second electrode can have a surface 150 that iscoated with a coating material 160. In some embodiments, such coatingcan be a conductive coating. The size of the pores and the thickness ofthe coating material can be configured so that inner volumes 170 of thepores are large enough for ions in the electrolyte to flow in and out.

Although FIG. 1 illustrates an embodiment in which the second electrodeis a porous material and the first electrode is a nonporous material,other configurations are contemplated as well. In one embodiment, thefirst electrode can be an anode formed of a nonporous material and thesecond electrode can be a cathode formed of a porous material. However,in other embodiments, both the anode and cathode can be formed fromporous materials. In still other embodiments, the first electrode can beporous and the second electrode can be nonporous. In some embodiments,the first electrode can be the cathode and the second electrode can bethe anode. In some embodiments, one or both electrodes can be coupled toa current collector (not shown).

In various embodiments, one of the electrodes in the hybridelectrochemical capacitor can operate as it would in an electric doublelayer capacitor (EDLC), and the other electrode can operate as it wouldin a battery. The EDLC-type electrode can form a double layer of chargedions on the surface of the electrode, and thereby store energy byphysical electric charge storage. The battery-type electrode canchemically react with ions in the electrolyte, such as byreduction/oxidation reactions, and thereby store energy through chemicalreactions. The combination of an EDLC-type electrode with a battery-typeelectrode allows the hybrid electrochemical capacitor to have qualitiesof both an EDLC and a battery. It should be noted that certaincombinations of materials and operating parameters can result in hybridelectrochemical capacitors with a beneficial combination of theadvantages of both EDLCs and batteries. However, many combinations ofmaterials and operating parameters can also result in hybridelectrochemical capacitors with many of the limitations and drawbacks ofEDLCs and batteries, but few of the advantages. The materials andcombinations disclosed in this description and the claims can be used tomake hybrid electrochemical capacitors with high energy density, highpower density, and other beneficial properties.

In some embodiments, a hybrid electrochemical capacitor can have ahigher voltage than conventional electrochemical capacitors. Forexample, in some cases the hybrid electrochemical capacitor can have avoltage of greater than 4 V. The energy density of the hybridelectrochemical capacitor is increased by increasing the electricalpotential over that of an electrochemical capacitor. Also, in someembodiments the hybrid electrochemical capacitor can maintain arelatively stable voltage throughout the discharging process. Forexample, in some cases more than 50% of the charge stored in the hybridelectrochemical capacitor can be discharged with a voltage drop of lessthan 1 V. This can make the hybrid electrochemical capacitor easier tointegrate into electrical systems than conventional capacitors, whichdrop in voltage linearly, from the maximum voltage to 0 volts, with thecharge lost during the discharging process. In addition, more of theenergy stored in the hybrid electrochemical capacitor can be utilizedcompared to a conventional capacitor, because after a conventionalcapacitor reaches a low voltage, such as about 1 V, the energy can nolonger be realistically utilized, resulting in waste of the remainingenergy.

An electrode of a hybrid electrochemical capacitor can be manufacturedfrom various porous materials as known in the art. In one embodiment,the electrode can be manufactured from porous silicon. Other materialsthat can be especially well-suited for electrodes are porous germanium,porous tin, and porous titanium dioxide. Possible advantages of usingporous silicon include its compatibility with existing silicontechnology, inexpensive raw material, and high storage capacity. In onespecific embodiment, the porous silicon can be doped. Porous germaniumenjoys similar advantages as a result of existing technology for thatmaterial, high storage capacity and, as compared to silicon, enjoys thefurther possible advantage that its native oxide (germanium oxide) iswater-soluble and so is easily removed (The native oxide that forms onthe surface of silicon reduces its conductivity which is an undesirableresult). Porous germanium is also highly compatible with silicontechnology. However, the raw material cost of germanium is significantlymore than silicon. Possible advantages of using porous tin, which is azero-band-gap material, include its enhanced conductivity with respectto certain other conductive and semiconductive materials.

Other materials can also be well-suited for porous electrodes. Forexample, suitable carbon-based materials can include activated carbon,carbon nanotubes, carbon nanofibers, graphene structures, and the like.Particulate materials comprising carbon, silicon, or other materials canbe used. In the case of particulate materials, it can be beneficial tohold the particles together with a conductive binder. In anotherembodiment, the substrate can be a nonporous material that istransformed into a porous material. Non-limiting examples of suchmaterials can include nano- or micro-structured materials, porous etchedmaterials, laser ablated materials, anodized materials, and the like.Suitable starting materials can include metals, semiconductors, silicon,carbon, silicon carbide, activated carbon, aluminum, and the like,including combinations thereof. Other materials can also be used for theporous structure, including alloys such as an alloy of silicon andgermanium, and metals such as copper, aluminum, nickel, calcium,tungsten, molybdenum, and manganese. Further specific examples of porousmaterials include polycrystalline Si, metallurgical grade silicon,silicon on insulator, Si—Ge alloys, GaAs, InP, GaN, AlGaAs, and BN.

In some embodiments the porous material is a single piece. In otherembodiment the porous material is comprised of an aggregate ofnon-porous elements (i.e. carbon nanotubes, graphene, ect.) that form anetwork of pores when bonded together either by a binder material ornaturally occurring surface forces such as van der waals forces).

The porous electrode can operate as an electric double layer capacitor.Generally, an electrode in a double layer capacitor operates by forminga double layer of electric charge along the surface of the electrode.When the electrode is charged, ions having an opposite charge areattracted toward the surface, forming a layer. The ions remainphysically adjacent to the electrode without reacting chemically withthe electrode material. Therefore, the electrode surface can be inert inrelation to the ions in the electrolyte in order for the electrode tooperate as an electric double layer capacitor. Current commerciallyavailable EDLCs are typically carbon based, although silicon based EDLCshave recently been contemplated. Silicon based EDLCs can employ a poroussilicon substrate material coated with a coating material that isconductive and inert. Since carbon is naturally conductive and highlyinert, no passivation is required for carbon based electrodes and noadditional layers are used. The layer of coating material in a siliconbased electrode typically has only one surface that is active and theelectrolyte forms a double layer on that surface. The other surface isinactive since it is in contact with the porous silicon.

Some embodiments may make use of very narrow pores in the porousmaterial. In certain embodiments, an electrolyte is introduced into thepores. In such embodiments the size of the pores can be sufficient toallow entry of the electrolyte. Certain electrolytes may have solvatedions on the order of 2 nanometers (nm). In at least one embodiment,therefore, a smallest dimension of each one of the pores is no less than2 nm so as to permit the electrolyte to flow freely along the entirelength of the pores.

In the same or another embodiment, the smallest dimension of each one ofthe pores is no greater than 1 micrometer (μm). This upper size limitfor the smallest dimension of the pores can be chosen for particularembodiments in order to maximize the surface area of the porousstructures of those embodiments. In some embodiments, the transfer ofions from the electrolyte to the electrode material is the kineticallylimiting reaction, and therefore maximizing the surface area canincrease the power. Smaller (e.g., narrower) pores lead to increasedoverall surface area for each electrode because a larger number of suchnarrower pores can fit into an electrode of a given size. Further, thepores' other dimensions, e.g., their lengths and/or shapes, can also bemanipulated in order to increase surface area or to achieve some otherresult. In embodiments where the porous electrode is an anode thatoperates by intercalation of ions, the increased surface area providedby the various pore sizes and configurations provides greateropportunity for intercalation of the porous material with ions andtherefore a greater charge capacity. In other embodiments the smallestdimension of the pores can be larger than 1 μm, and can be up to 10 μmor more. Although larger pores would decrease the surface area of theporous material, such larger pores can provide more interior space inwhich to grow or expand, or otherwise form additional structures, ifneeded.

Porous structures according to embodiments of the disclosure can befabricated with very precise and uniform pore size control. This allowsfast charging and also improves the capacity (pore size can be optimizedfor fast/efficient diffusion of ions through the pores to the maximumamount of surface area).

In some embodiments, a hybrid electrochemical capacitor can include acathode made of a porous material that is coated with a pseudocapacitivecoating material. In some cases, such as with a lithium metal anode, thecapacity density of the porous cathode can be less than the capacitydensity of the anode. Pseudocapacitive materials can be deposited ontothe cathode to increase the capacity of the cathode to more closelymatch the capacity of the anode. Examples of pseudocapacitive materialsinclude without limitation MnO₂, RuO₂, V₂O₅, VN, VC, Mo₂N, Mo₂C, W₂N,W₂C, CrN, poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy),poly(triaryl amine) (PTAA), polyaniline (PANI), and others.Pseudocapacitive materials can also include hydroxides.

In some embodiments, the first electrode can be an anode made fromalkali or alkaline metals including Mg, Na, other metals such as Zn, Al,Sn, alloys of these materials such as Na₂Ti₃O₇, Na₂Ti₆O₁₃, Si—Sn alloys,or materials alloyed with Mg. The second electrode can be a cathode madefrom any porous material that can act as an EDLC-type electrode. Forexample, porous carbon, passivated porous Si, or a porous cathode thatincludes a pseudocapacitive material can be used. Other porous materialscan also be prepared such as by plating a material onto porous siliconand then etching away the silicon. In one embodiment, the anode cancomprise magnesium, and the cathode can be a carbon-based cathodecomprising a binder and a conducting agent. In one specific embodiment,the binder can be sodium carboxymethyl-cellulose, and the conductingagent can be conductive carbon black such as SUPER C65. The electrolytecan be an electrolyte compatible with magnesium, containing Mg ions. Forexample, compatible electrolytes include 2-methyltetrahydrofuran withMgBr₂ and Mg(OCH₂(CH₃))₂.

Using magnesium as an anode can be beneficial for several reasons.First, magnesium does not react violently with water, as lithium does.Magnesium anodes can therefore be safer than lithium anodes, and can beused with aqueous electrolytes. Also, magnesium ions carry a charge of+2, so a magnesium anode can store twice as much charge per ion as alithium anode. However, magnesium has a more positive potential thanlithium and therefore the total voltage of a hybrid electrochemicalcapacitor with a magnesium anode can be less. In the past, magnesium hasnot been used extensively as an anode in batteries because of difficultyfinding effective cathodes that are compatible with magnesium anodes. Byusing an EDLC-type cathode in a hybrid electrochemical capacitor with amagnesium anode, the advantages of magnesium anodes can be utilizedwithout a need for finding a compatible battery-type cathode. Othermetals such as Na, Zn, Al, or Sn can be used as anodes in the same way,with appropriate electrolytes containing ions of the respective metals.

Alternatively, the anode can comprise lithium spinel structures such asLi₄Mn₅O₁₂, Li₄Ti₅O₁₂, and Li₂Mn₄O₉ with a spinel-type structure. Theelectrical potential of these materials is not as electronegative assome other materials, but is still low. One benefit using this materialis enhanced device stability and cyclability due to minimal deformationof the spinel material during operation.

Porous silicon can be used as an anode material in some embodiments. Insuch embodiments, the anode can be porous silicon that is pre-lithiated.In some embodiments silicon, porous silicon, or porous silicon particlesin a conductive matrix, such as carbon, can be used for the anode andlithium can intercalate into the anode. Alternatively, the anode cancomprise a porous transition metal nitride or oxide such as porous TiO₂,TiN, TaN, Ta_(x)O_(y), and/or TiO₂ coated porous silicon which can reactwith lithium to form lithium titanate. The electrical potential of thismaterial is not as low as some other anode materials, but is still low.By nano-engineering TiO₂, higher lithiation can be achieved to raise theenergy density on the anode side. Such porous silicon anodes can be usedtogether with cathodes made from porous silicon passivated with asuitable electrically conductive or pseudocapacative material. Also, insome embodiments, the cathode can comprise LiMn₂O₄, LiCoO₂, LiCoPO₄,LiMnPO₄, LiNiO₂, or combinations thereof.

In some embodiments that include porous silicon as an anode, the poroussilicon anode can be manufactured to have a target porosity. Suchporosity can be achieved using etching techniques, or other knowntechniques as known in the art. In some embodiments, the porouselectrode can expand during use, such as when a porous silicon electrodeis lithiated. The porosity generally allows for the expansion of theporous material during use.

In one embodiment, the porosity can be determined based on the designedvolume change of the system. For example, if an anode volume change isdesigned to be x %, then the porosity can be 1−[1/(1+(x %/100%)] orgreater. In one example, the porosity can range from 25% to 80%. In oneaspect, the porosity can be 50% or more. Other examples of porosityinclude 60% or more, 70% or more, or even 80% or more. Such poroussilicon anodes can be used together with cathodes that are made fromporous silicon passivated with a suitable electrically conductivematerial.

Referring to FIG. 2, in some embodiments a hybrid electrochemicalcapacitor 100 can have a separator 210 between the first electrode 110and the second electrode 120. The separator can prevent the electrodesfrom coming into contact with one another and causing an electricalshort. The separator can also be permeable to ions in the electrolyte130 so that the ions can flow back and forth between the electrodes. Theseparator can allow ions to pass through while electrically insulatingthe electrodes from one another (i.e., not allowing electrons to passthrough). In some embodiments, the electrolyte can be an organicelectrolyte and the separator can be made from a porous ceramic, apolymer film, or combinations thereof. Other examples of suitableseparator materials can include without limitation cellulose, includingwet-laid, PP non-woven, and microporous membrane (ePTFE or HDPE) basedmaterials. It should be noted that a separator is not always necessaryif the electrodes are positioned a sufficient distance apart from eachother to prevent electrical shorts and both electrodes are compatiblewith the electrolyte.

In some embodiments, a solid state electrolyte can act as both anelectrolyte and a separator. For example, in some cases the firstelectrode can comprise a reactive material such as lithium. If anaqueous electrolyte is used, then a solid state electrolyte can preventcontact between the lithium electrode and water in the aqueouselectrolyte.

In some embodiments, a hybrid electrochemical capacitor can include afirst electrode, a second electrode, and an electrolyte, wherein thefirst electrode comprises Mg, Na, Zn, Al, Sn, pre-lithiated carbon, Li,or combinations thereof; and the second electrode comprises a porousstructure formed out of a group IV semiconductor, a group III-Vsemiconductor, or combinations thereof. For example, in one specificembodiment, the first electrode can be a lithium metal anode and thesecond electrode can be a cathode made of porous silicon passivated withatomic layer deposited titanium nitride (ALD TiN). The electrolyte canbe an organic electrolyte solution such as a 1M solution of lithiumhexafluorophosphate (LiPF₆) in propylene carbonate (PC) or a 1M solutionof lithium perchlorate (LiClO₄) in PC. Other lithium salts and otherorganic solvents can also be used. For example, lithium salts caninclude lithium hexafluoroarsenate monohydrate (LiAsF₆), lithiumtetrafluoroborate (LiBF₄), and lithium triflate (LiCF₃SO₃). Othersuitable organic solvents include ethylene carbonate, (EC), diethylcarbonate (DEC), dimethyl carbonate (DMC), ethyl methylcarbonate (EMC),and acetonitrile. Other lithium-based anodes can also be used, includingalloys of lithium with other materials such as Li₄Ti₅O₁₂ or lithiumalloyed with carbon such as petroleum coke. In another specificembodiment, the anode can be Li₄Ti₅O₁₂ and the electrolyte can be LiPF₆in ethylene carbonate and dimethyl carbonate.

In some embodiments, the hybrid electrochemical capacitor can include anelectrode made of porous silicon passivated with an electricallyconductive coating material. Referring again to FIG. 2, in someembodiments the second electrode 120 can include a coating material 160that coats the surfaces 150 of the electrode that are in contact withelectrolyte 130. In cases where the electrode is made of silicon, thiscoating material can passivate the silicon to prevent the silicon fromreacting with the electrolyte. The coating material can form a layerwith any desired thickness. In some embodiments, the thickness of thecoating material can be less than 100 nm. In other embodiments, thethickness of the coating material can be less than 50 nm, less than 30nm, or less than 10 nm. In some embodiments, the thickness of thecoating material and the dimensions of the pores can be configured sothat ions from the electrolyte can flow into and out of the interiorvolumes 170 of the pores.

The coating material can be an electrically conductive material. In someembodiments, the coating material can include carbon, nitride, silicide,carbide, or combinations thereof. Graphene, graphene based composites,and carbon nano-structures can be used as coating material to both boostconductivity and add surface area. As an example, these can benanoparticles or nanowires of any suitable material (e.g., silicon orcarbon) or combination of materials (e.g., silicon germanium-with eithera silicon core or a germanium core), carbon nanotubes, silicon-coatedcarbon nanotubes, or the like. In some embodiments such nano-structurescan be coated, or partially coated, with an electrically conductive or apseudocapacitive coating. This coating can be a good electricalconductor (e.g., an appropriate metal, a silicide, or the like). Atleast some of the nanostructures can contain a dopant in order tofurther increase their electrical conductivity. Additionally, in someembodiments at least some of the nanostructures are coated with amaterial that prevents an electrochemical reaction between thenanostructures and the electrolyte.

Additionally, the coating material can include a pseudocapacitivematerial. The coating layer can be a homogeneous layer of a singlematerial in some embodiments, while in other embodiments the coatinglayer can include multiple layers of different materials. For example,in some embodiments the coating layer can include a first layer of anelectrically conductive material and a second layer of apseudocapacitive material. In some embodiments, the pseudocapacitivematerial can be a hydroxide. Other examples of pseudocapacitivematerials include MnO₂, RuO₂, V₂O₅, VN, VC, Mo₂N, Mo₂C, W₂N, W₂C, CrN,PEDOT, PPy, PTAA, PANI, and others.

In some embodiments, the volume of the second electrode can be greaterthan the volume of the first electrode. In some cases, the anodematerial can have significantly higher capacity than the cathodematerial. For example, lithium has a higher capacity density than poroussilicon. Therefore, it can be beneficial to make the cathode with alarger volume than the anode to balance the capacities of the anode andcathode. In some embodiments this is achieved by anodizing deeper intothe silicon or using a thicker layer of activated carbon as the cathode.

In some embodiments, a hybrid electrochemical capacitor can include afirst electrolyte and a second electrolyte. The first electrolyte can bea water-stable electrolyte, while the second electrolyte can be anaqueous electrolyte. The first electrode can be at least partiallyimmersed in the first electrolyte, and the second electrode can be atleast partially immersed in the second electrolyte. Two differentelectrolytes can be used in this way when the first electrode operatesbetter in non-aqueous electrolyte and the second electrode operatesbetter in aqueous electrolyte. For example, in embodiments with alithium anode, the lithium can be in contact with the water-stableelectrolyte, and the water-stable electrolyte can shield the lithiumanode from the aqueous electrolyte so that lithium does not react withwater in the aqueous electrolyte. As shown in FIG. 3, in someembodiments the electrolyte 130 can be a water-stable electrolyte incontact with the first electrode 110. The second electrolyte 310 can bean aqueous electrolyte in contact with the second electrode 120. In thisway, the hybrid electrochemical capacitor can operate with two differentelectrolytes selected to be compatible with the two electrodes. Thewater-stable electrolyte can include a gel electrolyte, a solid-stateelectrolyte, a non-aqueous electrolyte, or combinations thereof. In somecases, two solid state electrolytes and separators may be used forcathodes and anodes selectively. For example, in some cases the solidstate electrolytes can act as separators and can prevent electricalcontact without the use of another separator besides the solid stateelectrolytes. Two different solid state electrolytes can be used whereone electrolyte is more compatible with one electrode, and the otherelectrolyte is more compatible with the other electrode.

Another embodiment can include a mobile electronic device. The mobileelectronic device can include a housing enclosing a processing unit andan energy storage device electrically connected to the processing unitto provide power to the processing unit. The energy storage device cancomprise a hybrid electrochemical capacitor as described above. Thehybrid electrochemical capacitor can include a first electrode, a secondelectrode, and an electrolyte. In some embodiments of the mobileelectronic device, the first electrode can comprise Mg, Na, Zn, Al, Sn,or combinations thereof, and the second electrode can comprise a porousmaterial having a surface-area-to-volume ratio of at least 10 m²/cm³. Insome embodiments, the surface-area-to-volume ratio of the porousmaterial can be from about 10 m²/cm³ to about 5000 m²/cm³; in otherembodiments the ratio can be from about 100 m²/cm³ to about 2000 m²/cm³;and in other embodiments the ratio can be from about 300 m²/cm³ to about1000 m²/cm³. In other embodiments of the mobile electronic device, thefirst electrode can comprise Mg, Na, Zn, Al, Sn, pre-lithiated carbon,Li, or combinations thereof, and the second electrode can compriseporous silicon.

In some embodiments of the mobile electronic device, at least one of thefirst electrode and the second electrode can comprise porous silicon,porous carbon, graphene, a carbon nanowire, a carbon nanotube, porousGermanium, porous group III-V semiconductor, porous group IVsemiconductor, a pseudocapacitive material, or combinations thereof.Further, the electrodes can comprise any of the materials disclosedabove for use in electrodes of hybrid electrochemical capacitors.

In other embodiments of the mobile electronic device, the electrolytecan be a water-stable electrolyte, and the hybrid electrochemicalcapacitor can also include a second electrolyte that comprises anaqueous electrolyte. The first electrode can be at least partiallyimmersed in the electrolyte and the second electrode can be at leastpartially immersed in the second electrolyte. The water-stableelectrolyte can be a gel electrolyte, a solid-state electrolyte, or anon-aqueous electrolyte. The hybrid electrochemical capacitor in themobile electronic device can also include a separator. In someembodiments, the electrolyte can be an organic electrolyte and theseparator can comprise a porous ceramic, a polymer film, or combinationsthereof.

Hybrid electrochemical capacitors can be incorporated into a variety ofelectronic systems. For example, a hybrid electrochemical capacitor canbe integrated monolithically onto a silicon substrate or package. Anelectronic system having a monolithically integrated hybridelectrochemical capacitor can include a semiconductor substrate, one ormore electronic circuit elements, and at least one hybridelectrochemical capacitor. The electronic circuit element and the hybridelectrochemical capacitor are thus formed monolithically on thesemiconductor substrate. The electronic circuit element can include anytype of circuit element that can be beneficially combined with a hybridelectrochemical capacitor on a substrate. Non-limiting examples includeCPUs, GPUs, control units, integrated circuits, transistor elements,diodes, photodiodes, and the like. Additionally, the monolithicsubstrate can include electrical circuitry that provides electricalconnectivity between the hybrid electrochemical capacitor and theelectronic circuit element.

Additionally, in some embodiments multiple hybrid electrochemicalcapacitors can be combined to form systems having enhanced electricalproperties. In one aspect, for example, a high energy storage systemhaving enhanced operation voltage is provided. Such a system can includea plurality of hybrid electrochemical capacitors as have been described,where the plurality of hybrid electrochemical capacitors arefunctionally coupled together in series or in parallel depending onwhether higher voltage (series) or power (parallel) is desired. In someaspects such a system can be formed by bringing together hybridelectrochemical capacitors that have been manufactured as separateunits. In other aspects, the hybrid electrochemical capacitors can beformed together as a system during manufacture. It is contemplated that,in such cases, various structures can be shared between the capacitorsbeing constructed in series or parallel. For example, in one aspect apair of adjacent hybrid electrochemical capacitors can share adouble-sided electrode, or in some cases, a composite double-sidedelectrode.

Hybrid electrochemical capacitors can be integrated into mobile or otherelectronic devices to provide energy storage with rapid response. Thehybrid electrochemical capacitors can be used together with batteries orpotentially to replace batteries. Hybrid electrochemical capacitors canprovide high power for applications such as turbo modes inmicroprocessors. Unlike batteries, hybrid electrochemical capacitors canbe charged and discharged quickly because they do not rely on chemicalreactions to store energy. Further, they do not degrade significantlyover their lifetime, even when charged and discharged rapidly. Hybridelectrochemical capacitors are also less sensitive to temperature thanbatteries. Several applications for hybrid electrochemical capacitors invarious devices include: power for sleep/standby mode or backup powerfor memory; quick charging of electronic devices; turbo modes; cameraflashes; intermittent renewable energy sources (wind-turbines, solar/PVpanels, hydraulic power, or wave generators, for example); lowtemperature applications (hybrid ECs can be used from −25° C. to +60° C.with less than 5% energy loss versus 50% for batteries); energy storagefor energy harvesting devices; automotive applications such asregenerative braking, which provides a certain amount of recharging whenthe car decelerates; increased power density for up-hill or accelerativedriving; providing power to unlock car doors or lower windows in anemergency; and others.

Another embodiment can include a method of manufacturing a hybridelectrochemical capacitor. As illustrated in FIG. 4, the method 400 caninclude providing a silicon substrate 410, forming a porous region inthe silicon substrate 420, and forming a first electrode over the porousregion using a thin film deposition technique. With the first electrodedeposited over the porous region, the porous region can be a secondelectrode of the hybrid electrochemical capacitor 430. The firstelectrode can be formed from any of the electrode materials disclosedabove that can be deposited using a thin film deposition technique. Theporous region in the silicon substrate can also be modified prior todepositing the first electrode, such as by coating the porous siliconregion with a coating material as disclosed above or pre-lithiating theporous silicon region in embodiments where the porous silicon is apre-lithiated anode. Additionally, an electrolyte of any of the typesdisclosed above can be deposited on the porous silicon region beforeforming the first electrode over the porous region. A separator can alsobe deposited between the porous silicon region and the first electrode.

The porous silicon region can be formed by any known method, and anysuch method is considered to be within the present scope. In someembodiments, for example, the porous region can be formed via atechnique such as anodization, microelectromechanical systems (MEMS)processing including lithography, chemical etching, and the like, aswell as other known methods. Additionally, by varying the threedimensional characteristics of the porous region, the resulting hybridelectrochemical capacitor can be optimized to achieve higher energycapacity. Through such methods, the hybrid electrochemical capacitorscan be easily integrated into silicon technology and the form factor canbe adjusted for use in devices such as a typical package used formicrochips.

The porous silicon region can be coated with coating materials using avariety of techniques, and any known method capable of depositing suchmaterials on a porous silicon surface is considered to be within thepresent scope. For example, coating materials can be deposited by avariety of non-limiting methods, including complementarymetal-oxide-semiconductor (CMOS) processing methods, chemical vapordeposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD) growth, supercritical flow growth, hydrothermal growth,electroplating, spin on for polymers, and the like. Additionally,particulate materials can be deposited onto the porous silicon bymethods such as solution casting, electrophoresis, sintering, or thelike.

The first electrode can be deposited over the porous region by any ofthe above-identified deposition techniques as well. In some embodiments,the first electrode can be an anode and can be formed from any of theanode materials disclosed above. The anode can also be a porous materialthat is conductive and related to heat sinking.

A porous region in the silicon substrate can be defined as any surfacemodification that increases the surface area of the silicon substrate.In some aspects, a silicon substrate having a porous region can have amuch higher surface area as compared to a substrate lacking such porousregion. It is noted that any type of structuring to any degree thatincreases the surface area of the silicon substrate is considered to bewithin the present scope. In some cases, the porous region can comprisedistinct surface features that increase the surface area of thematerial. While such surface features can be of any size that isbeneficial for use in a hybrid electrochemical capacitor, in one aspectsurface features can have an average size of from about 2 nm to about100 microns. In another aspect, surface features can have an averagesize of from about 2 nm to about 300 nm. In yet another aspect, surfacefeatures can have an average size of from about 2 nm to about 80 nm.Non-limiting examples of surface feature types can include pillars,tubes, trenches, cones, pyramids, walls, pores, sponges, and the like,including appropriate combinations thereof. It is noted that themeasurement of average size of a given surface feature can varydepending on the feature. For example, vertically oriented surfacefeatures such as pillars, tubes, cones, and pyramids can be measuredfrom the base to pinnacle of the feature. For pores, on the other hand,average size can be measured as an average diameter of the pore, whiletrenches can be measured as the trench width. In some aspects, thestructured material can have a pore size of from about 30 nm to about300 nm. It is noted that the above applies for structured surfaces onmaterials other than silicon as well, such as, for example, porouscarbon materials.

In one example, a hybrid electrochemical capacitor can comprise a firstelectrode, a second electrode, and an electrolyte, wherein the firstelectrode comprises Mg, Na, Zn, Al, Sn, or combinations thereof, and thesecond electrode comprises a porous material having asurface-area-to-volume ratio of at least 10 m²/cm³.

In one example, the second electrode can comprise a porous materialhaving a surface-area-to-volume ratio from about 10 m²/cm³ to about 5000m²/cm³.

In one example, the second electrode can comprise a porous materialhaving a surface-area-to-volume ratio from about 100 m²/cm³ to about2000 m²/cm³.

In one example, the second electrode can comprise a porous materialhaving a surface-area-to-volume ratio from about 300 m²/cm³ to about1000 m²/cm³.

In one example, the second electrode can comprise porous carbon.

In one example, the second electrode can comprise a binder and aconducting agent.

In one example, the second electrode can be a single piece.

In one example, the second electrode can comprise a particulatematerial.

In one example, the particulate material can be in a binder.

In one example, the second electrode can comprise porous silicon, porousgermanium, porous group III-V semiconductor, porous group IVsemiconductor, graphene, a carbon nanowire, a carbon nanotube, orcombinations thereof.

In one example, the second electrode can comprise a pseudocapacitivematerial.

In one example, the first electrode can comprise magnesium and theelectrolyte can comprise Mg ions.

In one example, the hybrid electrochemical capacitor can furthercomprise a separator.

In one example, the separator can be a solid state electrolyte.

In one example, a hybrid electrochemical capacitor can comprise a firstelectrode, a second electrode, and an electrolyte, wherein the firstelectrode comprises Mg, Na, Zn, Al, Sn, pre-lithiated carbon, Li, orcombinations thereof, and the second electrode comprises a porousstructure formed out of a group IV semiconductor, a group III-Vsemiconductor, or combinations thereof.

In one example, the second electrode can comprise porous silicon.

In one example, the porous silicon can be coated with a coating materialwith a thickness less than 100 nm.

In one example, the coating material thickness can be less than 50 nm.

In one example, the coating material thickness can be less than 30 nm.

In one example, the coating material thickness can be less than 10 nm.

In one example, the coating material can be electrically conductive.

In one example, the coating material can comprise carbon, nitride,silicide, carbide, or combinations thereof.

In one example, the coating material can comprise titanium nitride.

In one example, the coating material can passivate surfaces of theporous silicon.

In one example, the coating material can be pseudocapacitive.

In one example, the pseudocapacitive coating material can comprise ahydroxide.

In one example, the second electrode can be configured to have a chargestorage capacity substantially matching a charge storage capacity of thefirst electrode.

In one example, the hybrid electrochemical capacitor can furthercomprise a second electrolyte, wherein the electrolyte is a water-stableelectrolyte, the second electrolyte is an aqueous electrolyte, the firstelectrode is at least partially immersed in the electrolyte, and thesecond electrode is at least partially immersed in the secondelectrolyte.

In one example, the electrolyte can comprise a gel electrolyte, asolid-state electrolyte, a non-aqueous electrolyte, or combinationsthereof.

In one example, the electrolyte can be a non-aqueous electrolyte.

In one example, the hybrid electrochemical capacitor can furthercomprise a separator.

In one example, the electrolyte can be an organic electrolyte and theseparator can comprise a porous ceramic, a polymer film, or combinationsthereof.

In one example, a mobile electronic device can comprise a housing, aprocessing unit, and an energy storage device, the energy storage devicecomprising a hybrid electrochemical capacitor, wherein the hybridelectrochemical capacitor comprises a first electrode, a secondelectrode, and an electrolyte, wherein either: (1) the first electrodecomprises Mg, Na, Zn, Al, Sn, or combinations thereof, and the secondelectrode comprises a porous material having a surface-area-to-volumeratio of at least 10 m²/cm³, or (2) the first electrode comprises Mg,Na, Zn, Al, Sn, TiO₂ pre-lithiated carbon, Li, or combinations thereof,and the second electrode comprises porous silicon.

In one example, at least one of the first electrode and the secondelectrode can comprise porous silicon, porous carbon, graphene, a carbonnanowire, a carbon nanotube, porous Germanium, porous group III-Vsemiconductor, porous group IV semiconductor, a pseudocapacitivematerial, or combinations thereof.

In one example, the electrolyte can be a water-stable electrolyte, thehybrid electrochemical capacitor can further comprise a secondelectrolyte, the second electrolyte comprising an aqueous electrolyte,and the first electrode can be at least partially immersed in theelectrolyte and the second electrode can be at least partially immersedin the second electrolyte.

In one example, the electrolyte can comprise a gel electrolyte, asolid-state electrolyte, a non-aqueous electrolyte, or combinationsthereof.

In one example, the electrolyte can be a non-aqueous electrolyte.

In one example, the mobile electronic device can further comprise aseparator.

In one example, the electrolyte can be an organic electrolyte and theseparator can comprise a porous ceramic, a polymer film, or combinationsthereof.

In one example, a method of manufacturing a hybrid electrochemicalcapacitor can comprise providing a silicon substrate, forming a porousregion in the silicon substrate, forming a first electrode over theporous region using a thin film deposition technique, the porous regionforming a second electrode of the hybrid electrochemical capacitor.

In one example, the first electrode can comprise LiMn₂O₄, LiCoO₂,LiCoPO₄, LiMnPO₄, LiNiO₂, or combinations thereof, and the method canfurther comprise pre-lithiating the second electrode.

The described features, structures, or characteristics may be combinedin any suitable manner in one or more embodiments. In this description,numerous specific details are provided, such as examples of layouts,distances, network examples, etc. One skilled in the relevant art willrecognize, however, that many variations are possible without one ormore of the specific details, or with other methods, components,layouts, measurements, etc. In other instances, well-known structures,materials, or operations are not shown or described in detail but areconsidered well within the scope of the disclosure.

While the forgoing examples are illustrative of the specific embodimentsin one or more particular applications, it will be apparent to those ofordinary skill in the art that numerous modifications in form, usage anddetails of implementation can be made without departing from theprinciples and concepts articulated herein. Accordingly, no limitationis intended except as by the claims set forth below.

Example 1

A hybrid electrochemical capacitor is prepared with a lithium metalanode and a cathode made from porous silicon passivated with ALD TiN.The electrolyte is propylene carbonate with 1M lithium perchlorate. Noseparator is necessary. Cyclic voltammetry measurements are shown inFIGS. 5A and 5B. Lithium is used as a reference electrode and thevoltage is cycled between 3 and 4 volts. Note that the data for everycycle illustrated (i.e., cycles 10, 20, 30, 40, and 50) lie nearly ontop of each other because there is no appreciable change from Cycle 10to Cycle 50. It may be difficult to distinguish between the cycles onthe graphs, but this is because the data remain nearly the same over the50 charge cycles. The purpose of the graphs is to illustrate thestability of the hybrid electrochemical capacitor after multiple cycles.The hybrid electrochemical capacitor shows little change after 50cycles, indicating that the electrodes have good stability. Also, duringdischarge almost all the charge stored in the capacitor is releasedbefore reaching 3 volts. This shows that most of the energy stored bythe capacitor can be utilized before the voltage drops too low for theenergy to be usable.

What is claimed is:
 1. A hybrid electrochemical capacitor comprising: afirst electrode; a second electrode; and an electrolyte; wherein: thefirst electrode comprises Mg, Na, Zn, Al, Sn, TiO2 or combinationsthereof; and the second electrode comprises a porous material having asurface-area-to-volume ratio of at least 10 m2/cm3.
 2. The hybridelectrochemical capacitor of claim 1, wherein the second electrodecomprises a porous material having a surface-area-to-volume ratio fromabout 10 m2/cm3 to about 5000 m2/cm3.
 3. The hybrid electrochemicalcapacitor of claim 1, wherein the second electrode comprises porouscarbon.
 4. The hybrid electrochemical capacitor of claim 3, wherein thesecond electrode comprises a binder and a conducting agent.
 5. Thehybrid electrochemical capacitor of claim 3, wherein the secondelectrode is a substantially solid material.
 6. The hybridelectrochemical capacitor of claim 1, wherein the second electrodecomprises a particulate material.
 7. The hybrid electrochemicalcapacitor of claim 6, wherein the particulate material is in a binder.8. The hybrid electrochemical capacitor of claim 1, wherein the secondelectrode comprises porous silicon, porous germanium, porous group III-Vsemiconductor, porous group IV semiconductor, graphene, a carbonnanowire, a carbon nanotube, or combinations thereof.
 9. The hybridelectrochemical capacitor of claim 1, wherein the second electrodecomprises a pseudocapacitive material.
 10. The hybrid electrochemicalcapacitor of claim 1, wherein the first electrode comprises magnesiumand the electrolyte comprises Mg ions.
 11. The hybrid electrochemicalcapacitor of claim 1, further comprising a separator.
 12. The hybridelectrochemical capacitor of claim 11, wherein the separator is a solidstate electrolyte.
 13. A hybrid electrochemical capacitor comprising: afirst electrode; a second electrode; and an electrolyte; wherein: thefirst electrode comprises Mg, Na, Zn, Al, Sn, TiO2 pre-lithiated carbon,Li, or combinations thereof; and the second electrode comprises a porousstructure formed out of a group IV semiconductor, a group III-Vsemiconductor, or combinations thereof.
 14. The hybrid electrochemicalcapacitor of claim 13, wherein the second electrode comprises poroussilicon.
 15. The hybrid electrochemical capacitor of claim 14, whereinthe porous silicon is coated with a coating material with a thicknessless than 100 nm.
 16. The hybrid electrochemical capacitor of claim 15,wherein the coating material is electrically conductive.
 17. The hybridelectrochemical capacitor of claim 15, wherein the coating materialcomprises carbon, nitride, silicide, carbide, or combinations thereof.18. The hybrid electrochemical capacitor of claim 15, wherein thecoating material comprises titanium nitride.
 19. The hybridelectrochemical capacitor of claim 15, wherein the coating materialpassivates surfaces of the porous silicon.
 20. The hybridelectrochemical capacitor of claim 15, wherein the coating material ispseudocapacitive.
 21. A mobile electronic device comprising: a housing;a processing unit; and an energy storage device, the energy storagedevice comprising a hybrid electrochemical capacitor, wherein the hybridelectrochemical capacitor comprises: a first electrode; a secondelectrode; and an electrolyte; wherein either: (1) the first electrodecomprises Mg, Na, Zn, Al, Sn, or combinations thereof, and the secondelectrode comprises a porous material having a surface-area-to-volumeratio of at least 10 m2/cm3; or (2) the first electrode comprises Mg,Na, Zn, Al, Sn, pre-lithiating carbon, Li, or combinations thereof, andthe second electrode comprises porous silicon.
 22. The mobile electronicdevice of claim 21, wherein at least one of the first electrode and thesecond electrode comprises porous silicon, porous carbon, graphene, acarbon nanowire, a carbon nanotube, porous Germanium, porous group III-Vsemiconductor, porous group IV semiconductor, a pseudocapacitivematerial, or combinations thereof.
 23. The mobile electronic device ofclaim 21, wherein: the electrolyte is a water-stable electrolyte; thehybrid electrochemical capacitor further comprises a second electrolyte,the second electrolyte comprising an aqueous electrolyte; and the firstelectrode is at least partially immersed in the electrolyte and thesecond electrode is at least partially immersed in the secondelectrolyte.
 24. The mobile electronic device of claim 23, wherein theelectrolyte comprises a gel electrolyte, a solid-state electrolyte, anon-aqueous electrolyte, or combinations thereof.
 25. The mobileelectronic device of claim 21, wherein the electrolyte is a non-aqueouselectrolyte.
 26. The mobile electronic device of claim 21, furthercomprising a separator.
 27. The mobile electronic device of claim 26,wherein the electrolyte is an organic electrolyte and the separatorcomprises a porous ceramic, a polymer film, or combinations thereof.